I keep seeing a pale man in a black suit. someone help please!! *long*?

about a week ago i was coming off of a bad dxm trip when as i was looking out at the sunrise(with my friends in the other room playing a game) when i noticed a man staring back at me. He was just standing there in the middle of the road looking straight at me. I went to get my friends, but when i came back he was gone... I though it was just the drug but a couple days later he re-apperaed only this time in the middle of the night as i was getting water i saw him in the mirror but only for a brief second as the fright was enough to make me flee from the room... i keep seeing him more and more and each time he is closer. I am 17 very scared and now that i saw him at the foot of my bed i feel i cant ignore this any longer. please i need a no bullshit answer of what he or it might be PLEASE SOMEONE HELP!!!........... it almost reminds me of a person named G-man from a game called half life if that helps at all... oh and i see him in my dreams but the dreams he appears usually turn into nightmares that ive recorded in a journal.